The present invention relates to developing machines for radiation-sensitive material. More particularly, the invention relates to improvements in means for circulating a liquid in a tank or another suitable vessel which is utilized in a developing machine for photosensitive or other radiation-sensitive materials.
It is well known to utilize in a developing machine for radiation-sensitive material a series of successive vessels through which the exposed material advances to be subjected to treatment by different liquids. For example, when the photosensitive material is a web or strip of photographic film or photographic paper, such web or strip will advance seriatim first through a developing bath, thereupon through a fixing bath and finally through a rinsing bath on its way toward and through a drying chamber. As a rule, the rinsing bath comprises an open-top tank or another suitable vessel with an outlet opening in the bottom wall thereof, and a system which circulates the fluid leaving the interior of the vessel by way of the outlet opening back into the upper portion of the supply of liquid in the vessel. The circulating system comprises a pump which draws the liquid through the outlet opening and causes the liquid to flow to a level above the upper surface of the supply of liquid in the vessel.
The situation is analagous in automatic or semiautomatic developing machines for X-ray films. In such machines, too, the exposed film is transported through developing, fixing and rinsing baths prior to drying for the purpose of removing the surplus of moisture from its sides. The function of the rinsing bath is to wash away salts and ions which tend to adhere to the radiation-sensitive emulsion. Such constituents are caused to contact the X-ray film during preceding chemical treatment in the developing and fixing vessels. Furthermore, rinsing is desirable and advantageous because it enhances or prolongs the useful life or storage life of fully exposed and developed X-ray films.
It is further well known that the liquid which fills the rinsing tank tends to accumulate suspended matter which floats in the filtered body of liquid, normally water. Such suspended matter can exert an adverse influence upon the X-ray film. The suspended matter includes remnants of gelatin which is washed out of the emulsion and/or algae which penetrate into the vessel with inflowing water and utilize the remnants of gelatin as an ideal breeding ground for rapid multiplication in the interior of the rinsing vessel. The deleterious effects of such microorganisms are twofold. First of all, the suspended matter is likely to form on the developed film spots which tend to obscure the image on the X-ray film. It is quite likely that a spotted fully developed X-ray film will lead to inaccurate diagnoses and unsatisfactory or improper treatment of patients. Secondly, the suspended matter is likely to deposit on the film transporting equipment, such as rollers, whereby the deposits adversely affect the configuration of the film-contacting surfaces of the rollers. This can lead to problems in connection with automatic transport of X-ray films through the vessels in the developing machine.
There exist many proposals to eliminate the presence or spreading of suspended matter in rinsing tanks of automatic developing machines for radiation-sensitive material. For example, it was proposed to add algicides at regular intervals. Such substances are designed to prevent further multiplication of algae. However, it has been found that algae which are present in the vessel at the time of admission of such substances are not affected at all so that the failure of an attendant to admit algicides at regular intervals can entail a pronounced growth of algae with the aforediscussed consequences. Furthermore, the cost of algicides is extremely high. Moreover, the remnants of gelatin are not affected by the addition of such substances.
Another prior proposal to prevent the development and multiplication of suspended matter includes continuous replacement of the contents of a rinsing tank. However, this is extremely costly, not only because of the consumption of excessive quantities of water but also as regards the energy requirements of the equipment which effects circulation of water, namely, the evacuation of water from the interior of the vessel and continuous admission of fresh water to replace the evacuated liquid.
It is also known to provide the rinsing vessel of a developing machine with a shutoff valve which is opened as soon as the developing machine is brought to a standstill. When the developing machine is started again, the shutoff valve is closed and the attendants open one or more additional valves which admit fresh rinsing liquid into the interior of the vessel. The filling of the vessel is monitored by electrodes which close the valve of valves for admission of fresh rinsing liquid as soon as the upper surface of the accumulated liquid in the rinsing vessel has risen to a predetermined level. As a rule, the shutoff valve and the fluid-admitting valve or valves are solenoid-operated valves which are quite sensitive and expensive. Relatively inexpensive solenoid-operated valves define rather small paths for the flow of liquids therethrough. Consequently, such valves are highly likely to be clogged by suspended matter after a relatively short period of use. This applies in particular to the aforementioned shutoff valve. On the other hand, solenoid-operated valves which provide relatively large passages for the flow of a liquid therethrough are quite complex and expensive.